Multilayer composite armour

ABSTRACT

The invention relates to the area of armor and in particular to a multilayer armor plate having a composite layer ( 15, 25, 35 ) containing a first material made of a metal or an alloy and a second material ( 1, 11, 21, 31 ) where the second material is porous and in that said metal or said metal alloy is infiltrated into some or all of the pores of said second material ( 1, 11, 21, 31 ), and characterized in that a cage ( 4, 14, 24, 34 ) made of plates ( 5 ) having openings ( 6 ) contains said first and second materials and in that the cage ( 4, 14, 24, 34 ) is itself coated, at least partly, with said infiltration metal or alloy, the melting point of the cage material being higher than that of the infiltration metal or alloy.

BACKGROUND OF THE INVENTION

[0001] The invention relates to the area of armor and in particularmultilayer armor having a composite layer containing a first material,for example a ceramic, and a second material, such as a metal or metalalloy.

[0002] Ceramic has been known for its ballistic performance for a numberof years, either as a material placed at the front face of a piece ofarmor or embedded in the metal material to increase overall armoreffectiveness.

[0003] The most significant work in the area of cast composite armor hasrelated mainly to production of armor with a series of ceramicreinforcements distributed in a metal matrix, generally obtained by aprocess related to casting.

[0004] These types of armor, although their performance is satisfactory,are generally difficult to fabricate and do not have guaranteedprotection effectiveness that is identical for all angles of attack, forall impact points on the front face, and also have low performance withmultiple impacts (two successive shots striking the same impact zone).

[0005] Moreover, in view of the nature and shape of the reinforcementbodies used, and in view of the implementation difficulties, the cost ofthe protection thus obtained is generally high by comparison to armorcomposed of monolithic materials.

[0006] Finally, the exceptional compressive strength performance ofceramics is not fully exploited due to the confinement configurationsrecommended by the various inventors, which do not exhibit an optimalconfiguration.

[0007] For example, McDougal et al., in their U.S. Pat. No. 3,705,558,provide a light armor composed of a layer of ceramic balls placed incontact but such that a small gap between the balls allows for a liquidmetal coating to pass through. Various configurations are then possible,such as, the ceramic balls are enclosed in a stainless steel pouch, orthey are covered with a nickel layer and then attached to an aluminumplate. The technique proposed by McDougal et al. has been criticized forits implementation difficulty and the risk inherent in the process ofdamaging the ceramic by thermal shock during the liquid metal coatingphase. Moreover, in the casting phase, the technique recommended byMcDougal et al. sometimes leads to unwanted movement of one ballrelative to another. This unexpected movement affects armoreffectiveness locally, and for this reason U.S. Pat. No. 4,158,338describes a strong wall panel containing hard, and thus, nonporousceramic particles, disposed during manufacture in a cage that holds themin position, and having holes through which is injected a liquefiedelastomer whose temperature is unable to damage the ceramic particles.U.S. Pat. No. 4,534,266, which describes a method of obtaining a regularnetwork of interconnected metal spheres that receive ceramic insertssubsequently embedded by the liquid metal during the casting stage, isalso known.

[0008] Other patents, such as, for example, U.S. Pat. No. 5,194,202,U.S. Pat. No. 4,415,632, DE 3924267, and DE 3837378 describe armorhaving a composite layer containing a first material composed of a metalor metal alloy and a second material and characterized in that thesecond material is porous and in that the metal or the alloy isinfiltrated into all or some of the pores of the second material.

[0009] However, such an armor cracks when struck by a projectile andwhen other plates made of metal, for example, are associated therewithby cementing or welding, separations occur between the plates which isdetrimental to the integrity and strength of the whole or the weldsbreak due to shear forces, leading once again to a reduction in theintegrity and strength of the whole.

SUMMARY OF THE INVENTION

[0010] The goal of the invention is to remedy the aforesaid difficultiesby providing a light, effective armor that is easy to fabricate, hasunparalleled integration flexibility, and has no weaknesses in integrityor strength in the event of cracking of the composite layer.

[0011] The solution provided is a multilayer armor having a compositelayer containing a first material made of a metal or an alloy and asecond material where the second material is porous and the metal or themetal alloy is infiltrated into some or all of the pores of the secondmaterial, wherein a cage made of plates having openings contains thefirst and second materials and in that the cage itself is coated, atleast partly, with the infiltration metal or alloy, the melting point ofthe cage material being higher than that of the infiltration metal oralloy.

[0012] According to another additional feature, the cage is entirelycoated with the infiltration metal or alloy.

[0013] According to another feature, the void ratio of the ceramic isbetween 0.1% and 80%.

[0014] According to another feature, the ceramic is partly or entirelycomprised of at least one of the following ceramics: recrystallized SiCand/or other types of ceramics, such as SiC—SiN, SiC—SiO₂, SiN, Al₂O₃,AlN, and Si₃N₄.

[0015] According to a particular feature, the ceramic is partly orentirely comprised of recrystallized silicon carbide.

[0016] According to another feature, the cage contains severalsuperimposed or juxtaposed reinforcing bodies made of infiltrated porousceramic.

[0017] According to another feature, the cage is made of metal or alloy.

[0018] According to a particular feature, the cage is made partly orentirely of one of the following metals or their alloys: iron, steel,copper, zinc, aluminum, magnesium, beryllium, or titanium.

[0019] According to one feature, the metal or the alloy infiltrated intothe pores of the ceramic is made partly or entirely of aluminum,magnesium, beryllium, or titanium.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Other advantages and features of the invention will appear in thedescription of various embodiments of the invention with reference tothe attached figures:

[0021]FIG. 1 is a perspective view of one example of a porousreinforcing body designed to enter into the composition of armoraccording to the invention;

[0022]FIG. 2 is a perspective view of one example of a metal cagedesigned to contain the porous reinforcing body;

[0023]FIG. 3 is a vertical section through a first embodiment of armorin which the porous reinforcing body forms only one body in the cage;

[0024]FIG. 4 is a vertical section through a second embodiment of armorcontaining several juxtaposed porous reinforcing bodies;

[0025]FIG. 5 is a vertical section through a third embodiment of armorcontaining several superimposed porous reinforcing bodies;

[0026]FIG. 6 shows one application of the invention for protection of aperson;

[0027]FIG. 7 shows one application of the invention to a vehicle forprotection of its occupants; and

[0028]FIG. 8 shows one application of the invention to an armoredvehicle for protection of its occupants.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029]FIG. 1 is a perspective view of an example of a body 1 made ofporous reinforcing material designed to enter into the composition ofthe armor. This body 1 is parallelepipedic in shape and is a ceramic. Itis made of recrystallized silicon carbide. Its void ratio is 15%. Thisbody has two large transverse surfaces 2 and small lateral surfaces 3.

[0030]FIG. 2 is a perspective view of an example of a metal cage 4designed to enclose said body 1 made of porous reinforcing material.This cage 4 is composed of steel plates 5 having regularly disposedcircular openings 6. These plates 5 are welded together to form a cage 4inside which the body 1 made of porous reinforcing material can bepositioned, at least one of the faces of the parallelepiped being weldedonce the porous body 1 has been placed inside cage 4.

[0031] The dimensions of the cage 4 and the porous body 1 are such thatthere is several millimeters or even more of play between one of thetransverse faces 2 of the porous body and the corresponding insidelateral face of cage 4. On the other hand, the play is practically zerobetween the lateral surfaces 3 of porous body 1 and the correspondinginside surfaces of cage 4.

[0032]FIG. 3 is a vertical section through an example of armor 19wherein the face exposed to the munition is called the front face 10while the opposite face 12 is called the rear face.

[0033] The armor 19 is of the multilayer composite type. It has a firstlayer 13 that is thin—several millimeters—and made of infiltrationmetal, in this case aluminum, then a composite 15 layer comprised of acage 14 containing a porous reinforcing body 11 made of recrystallizedsilicon carbide infiltrated and coated with the infiltration metal, andfinally a third layer 16 that is thick—several centimeters—consisting ofinfiltration metal.

[0034] It will be noted that the porous ceramic infiltration metal notonly infiltrates the pores of the ceramic but also coats the composite15, the thickness of this coating being small on the front face 10 andthe lateral faces 17 of cage 14 and thick on the rear face 12 of thearmor.

[0035]FIG. 4 is a vertical section through another example of an armor29 according to the invention.

[0036] The face exposed to the munition is called the front face 20while the opposite face 22 is called the rear face.

[0037] This armor 29 is of the multilayer composite type. It has a firstlayer 23 that is thin—several millimeters thick—and made of infiltrationmetal, in this case magnesium, then a composite comprised of a cage 24containing several juxtaposed porous reinforcing bodies 21 made ofalumina Al₂O₃ infiltrated and coated with the infiltration metal, andfinally a third layer 16 that is thick—several centimeters—consisting ofinfiltration metal.

[0038]FIG. 5 is a vertical section through another example of an armor39 according to the invention.

[0039] The face exposed to the munition is called the front face 30while the opposite face 32 is called the rear face.

[0040] This armor 39 is of the multilayer composite type. It has a firstlayer 33 that is thin—several millimeters thick—and made of infiltrationmetal, in this case titanium, then a composite comprised of a cage 34containing several superimposed porous reinforcing bodies 31, one madeof recrystallized silicon carbide with a void ratio of 21% and the otherof Si₃N₄ with a void ratio of 11%, both being infiltrated and coatedwith the infiltration metal, and finally a third layer 36 that isthick—several centimeters—made of infiltration metal.

[0041] The components entering into the fabrication of the invention aredeliberately chosen from the family of mass-produced industrial productsto attain the objective of low cost while meeting the objectives ofperformance, weight, ease of integration, and resistance tomulti-impacting presented above.

[0042] Thus, the material of the porous ceramic reinforcing body may,for example, be recrystallized silicon carbide (SiC) but also othertypes of ceramics, such as SiC—SiN, SiC—SiO₂, SiN, Al₂O₃, AlN, andSi₃N₄. The porosity of the reinforcing body must enable the infiltrationmetal to penetrate most or all of the pores to create an intimate bondbetween the two components and establish a state of local residualstresses generated by the differences in coefficient of thermalexpansion between the ceramic and the infiltration metal. Because thecoefficient of thermal expansion of the ceramic is extremely low (a few10⁻⁶/K), the ceramic material infiltrated by a metal (whose expansioncoefficient is between 2 and 10 times higher) has its expansioncoefficient fixed almost solely by the ceramic, which generates internalstresses in the material. The void ratio may typically be about 10 to20%, but good performance may also be achieved with lower void ratios,typically 10% and down to values less than 0.1%, or, on the contrary,higher such as 20 to 40%, for example. The void ratio, as explainedabove, is directly linked to the level of internal stresses reached inthe ceramic after infiltration by the metal and is, hence, to somedegree linked to the ballistic performance of the armor when impacted bya given munition. The armor will thus be optimized for a specificaggressor by choosing the most suitable void ratio.

[0043] The reinforcing material is contained in a cage. This cage ismade of a steel-type metal alloy so that it is easy to fabricate (inparticular the material is weldable) and inexpensive. However, othermetals, such as copper, zinc, iron, aluminum, magnesium, beryllium, ortitanium or another other similar metal or an alloy of these metals, canbe used for fabricating the cage as long as the chemical and physicalcompatibilities between the reinforcing material, the cage, and theinfiltration metal permit. The cage must be designed to contain thereinforcing material and easily enable passage of the liquid metalduring the infiltration phase. Further, the melting point of thematerial of which the cage is made must be greater than the meltingpoint of the infiltration metal or alloy.

[0044] The cage has a dual role. During the armor fabrication phase, thecage enables the reinforcing material to be located in one part of themold, and prevents the reinforcing material from cracking by aconfinement effect when the armor is impacted by the munition. When aprojectile strikes the ceramic/metal or alloy composite, the latter maybe cracked; the presence of the plates of which the cage is made limitsexpansion of the composite, hence the likelihood that it will crack isreduced, and even if it should crack, the cage deflects the crack,propagating it to the nearest opening in the cage. Thus, cracking isvery limited and the integrity of the armor is unimpaired.

[0045] It should be noted that for deflection of the crack to occur, theratio between the surface areas of openings 4 to that of the cage,namely its front, rear, and lateral faces, must be less than 75%.

[0046] The infiltration material is preferably a low-density metal or analloy of the low-density metal, such as aluminum, magnesium, orberyllium, but, for certain armor configurations, it may be useful toemploy other metals or alloys of these metals.

[0047] The invention calls for the cage containing the reinforcingmaterial to be fully embedded in the infiltration material. It ispreferable to locate the cage containing the reinforcing material nearthe front face of the armor (namely the face supposed to undergo impactby the munition) while taking care to provide a thin layer ofinfiltration material between the armor surface and the cage. The armormay be designed with a fairly large volume of infiltration material atthe rear face (namely the side opposite the side attacked) so that thismaterial can deform by a plastic deformation process and eventuallyabsorb the incident energy of the projectile.

[0048] The armor presented here is made by any known infiltrationprocess such as for example squeeze casting, casting, and pressureinfiltration (plunger or gas). In all these processes, the infiltrationmaterial is first heated to melting point to acquire sufficient fluidityand is then placed in the presence of the cage containing thereinforcing material. Pressure application, and preheating thereinforcing material, are two methods of facilitating infiltration ofthe metal into the reinforcement.

[0049] One method of manufacturing armor 19 according to the inventioncan be the following:

[0050] aluminum metal is heated in a furnace until the metal melts;

[0051] a metal cage is prepared in two weldable steel half-shellsprovided with many holes;

[0052] a porous recrystallized SiC ceramic plate is cut to dimensionsslightly less than those of the cage;

[0053] a SiC silicon carbide plate is inserted into the cage then closedwith several weld spots;

[0054] the cage+SiC plate assembly is preheated in a furnace;

[0055] the cage+SiC plate assembly is inserted into a squeeze castingmold;

[0056] liquid metal is poured over the cage+SiC plate assembly andpressure is applied to facilitate penetration of the liquid metal intothe pores of the silicon carbide plate and through the cage;

[0057] the assembly is cooled under controlled-temperature conditions;and

[0058] the assembly is unmolded.

[0059] This process has also been used to make an armor plate accordingto the invention with the goal of protecting part of a light vehicle.The reinforcing material used is in the form of three porous ceramicplates whose specifications are given below:

[0060] Type of ceramic: recrystallized silicon carbide (SiC);

[0061] Density: 2.6 to 2.7 g/cm³;

[0062] Void ratio: 15 to 19%;

[0063] Tensile strength at 20° C.: 90 to 100 Mpa;

[0064] Tensile strength at 1300° C.: 100 to 110 Mpa;

[0065] Young's modulus: 230 Gpa;

[0066] Thermal conductivity: 30 W/m/K;

[0067] Coefficient of thermal expansion: 10⁻⁶/K; and

[0068] Plate size: 150 mm×75 mm×8 mm.

[0069] This ceramic is a widely available product used, in particular,as an abrasion material for milling industrial tools.

[0070] The cage is obtained by bending and welding a 2 mm thick weldablesteel sheet provided with circular holes. The dimensions of the cage are152 mm×77 mm×26 mm so that it can accept the three ceramic plates.

[0071] The infiltration material used is a classical foundry alloy ofthe aluminum-silicon type. The technique used for the casting phase issqueeze casting.

[0072] Armor according to the invention can be dimensioned to protect aperson directly when used, for example, as a bullet-proof vest and as ahelmet as shown in FIG. 6, or to protect land systems such as wheeledvehicles, tracked vehicles, shelters, infrastructures, movable bridges,etc. as shown in FIGS. 7 and 8, or flying craft such as airplanes,helicopters, drones, missiles, etc., or marine systems such as surfaceships, submarines, crossing equipment, etc. against all types ofprojectiles, fragments, and shards.

[0073] The invention thus includes any type of composite armor andballistic armor containing one or more porous ceramic bodies enclosed ina metal cage, the entire assembly being infiltrated with a metal.

[0074] Depending on the application in view, the dimensioning of thesolution may combine variants of the following parameters:

[0075] nature of infiltration metal material;

[0076] nature of porous reinforcing material;

[0077] nature of metal material of which the cage is composed;

[0078] dimensions of porous reinforcing material;

[0079] number of elements of porous reinforcing material enclosed in thecage;

[0080] dimensions of cage (thickness of cage walls may be infinitelysmall);

[0081] proportions of the various components in terms of weight andvolume; and

[0082] armor geometry (may be parallelepipedic, curved, tubular, orother).

[0083] Several elements must be taken into consideration to illustratethe value of the invention.

[0084] First, a weight advantage. The components of the invention enablethe armor to be ranked as light armor comparable in performance to thereference aluminum armor (7020 alloy). Traditional protection solutionsfor light vehicles, such as automobiles, combat vehicles, transportvehicles, airplanes, helicopters, etc., employ panels severalmillimeters thick made of steel or titanium, and are hence heavier thanthe proposed solution.

[0085] The second advantage resides in the performance of the inventionagainst an extensive threat range. Of course, depending on theformulation used for the armor, it can be tailored to the type of threatby adjusting the weight-performance ratio. However, for a standardformulation, such as that referred to above, the armor plate providestotal protection against projectiles of any weight with impactvelocities of 500 to 1000 meters/second. Moreover, this formulation iswell below the 40 to 100 kg/m² range. This range corresponds to theweight of the protective equipment normally used on light vehicles.

[0086] The third advantage has to do with the integration flexibility ofthe invention. In its standard formulation, the armor can assume all theusual integration configurations of classical armor, namely:

[0087] the armor can be “applied,” i.e. applied to the structure to beprotected by any classical method, such as welding, cementing, bolting,adhesion, etc., as shown in FIG. 8;

[0088] the armor can be built directly into the structure for parts madeby a casting method such as openers, hoods, bodies, fenders, doors,roofs, floors, wheel rims, etc., as shown in FIG. 7; and

[0089] in the case of the “bullet-proof vest” or “flexible armor” typeapplications, the protection can easily be integrated into a classicalgarment configuration by a mosaic of plates, as shown in FIG. 5.

[0090] The fourth advantage of the invention is cost-related. Theinvention uses low-cost components and a low-cost manufacturingtechnique and procedure enabling mass production with no particularproduction constraints.

[0091] The fifth advantage resides in the ability of the invention toprovide total protection even in the case of successive impacts on asingle armor area (multi-impacting).

[0092] With regard to the particular case of flexible armor of the“bullet-proof vest” type as described for example in U.S. Pat. Nos.4,090,005 and 5,972,819, it is known that for the highest aggressionlevels the risks of injury are high for the wearer of the protectioneven though the munition is stopped. This damage is due to the effectsof indentation of the vest into the body, caused by insufficientdistribution of the impact force over the surface. The present inventionlimits these risks of rear-face damage by distributing the impact forcewidely.

[0093] Of course, numerous modifications may be made to the embodimentexample described above without departing from the framework of theinvention. Thus, a metal cage with an extremely small wall thickness maybe used, and the same metal or metal alloy may be chosen for theinfiltration material and for the cage.

1. Multilayer armor comprising: a composite layer containing a firstmaterial made of a metal or an alloy and a second material where thesecond material is porous said metal or said metal alloy is infiltratedinto some or all of the pores of said second material; and a cage madeof plates having openings, the cage contains said second material andthe cage itself is coated, at least partly, with said infiltration metalor alloy, the melting point of the cage material being higher than thatof the infiltration metal or alloy.
 2. Armor according to claim 1,wherein the cage is entirely coated with said infiltration metal oralloy.
 3. Armor according to claim 2, wherein the cage has two principalfaces and four lateral faces, wherein the thickness of this coating isgreater on one of the principal faces than on the other principal faceand greater than on the lateral faces.
 4. Armor according to claim 3,wherein the thickest coating thickness is a few centimeters.
 5. Armoraccording to claim 3, wherein the coating thickness on the lateral facesand on one of the principal surfaces is a few millimeters.
 6. Armoraccording to claim 2, wherein the ratio between the surface area ofopenings to that of the cage is less than 75%.
 7. Armor according toclaim 1, wherein said second material is comprised of a ceramic whosevoid ratio is between 0.1% and 80%.
 8. Armor according to claim 2,wherein the ceramic is partly or entirely comprised of at least one ofthe following ceramics: recrystallized (SiC) and/or other types ofceramics such as SiC—SiN, SiC—SiO₂, SiN, Al₂O₃, AlN, and Si₃N₄.
 9. Armoraccording to claim 7, wherein the ceramic is partly or entirelycomprised of recrystallized silicon carbide.
 10. Armor according toclaim 1, wherein the cage contains several superimposed or juxtaposedreinforcing bodies made of infiltrated porous ceramic.
 11. Armoraccording to claim 1, wherein the cage is made partly or entirely of oneof the following metals or their alloys comprised of iron, steel,copper, zinc, aluminum, magnesium, beryllium, or titanium.
 12. Armoraccording to claim 1, wherein said metal or said alloy infiltrated intothe pores of the second material is made partly or entirely of amaterial comprised of aluminum, magnesium, beryllium, or titanium. 13.Armor according to claim 4, wherein the coating thickness on the lateralfaces and on one of the principal surfaces is a few millimeters. 14.Armor according to claim 4, wherein the ratio between the surface areaof openings to that of the cage is less than 75%.
 15. Armor according toclaim 14, wherein said second material is comprised of a ceramic whosevoid ratio is between 0.1% and 80%.
 16. Armor according to claim 15,wherein the ceramic is partly or entirely comprised of at least one ofthe following ceramics: recrystallized (SiC) and/or other types ofceramics such as SiC—SiN, SiC—SiO₂, SiN, Al₂O₃, AlN, and Si₃N₄. 17.Armor according to claim 9, wherein the cage contains severalsuperimposed or juxtaposed reinforcing bodies made of infiltrated porousceramic.
 18. Armor according to claim 3, wherein the cage is made partlyor entirely of one of the following metals or their alloys comprised ofiron, steel, copper, zinc, aluminum, magnesium, beryllium, or titanium.19. Armor according to claim 6, wherein the cage is made partly orentirely of one of the following metals or their alloys comprised ofiron, steel, copper, zinc, aluminum, magnesium, beryllium, or titanium.20. Armor according to claim 6, wherein said metal or said alloyinfiltrated into the pores of the second material is made partly orentirely of a material comprised of aluminum, magnesium, beryllium, ortitanium.